The present invention relates to a decompression apparatus for an internal combustion engine designed to make starting of the engine easier in such a manner that at least either an intake valve or an exhaust valve is forcedly opened at engine starting and the valve open condition is automatically terminated after the engine starts.
Such a decompression device has been known which is automatically operated to open either an intake valve or an exhaust valve to a small extent to reduce the compression pressure in combustion chambers during starting and thereby to reduce the starting load of the engine.
Japanese Utility Model Publication No. 50-7381 discloses an automatic decompression device which is operated by the centrifugal force of a weight and automatically reduces pressure in a combustion chamber during the starting of an engine. In the known device, the decompression device needs not only many parts because of complexity in construction but also much time to make and assemble it.
Particularly in an engine whose output shaft, power-take-off (PTO) shaft, is one end of a camshaft, it is difficult to provide a releasing lever on the camshaft between the output shaft portion and a cam of the camshaft since the diameter of the output shaft must be rather large.